1. Field of the Invention
The invention relates to a positioning device for a drawer rail, especially to a positioning device that is simple but able to provide a secure positioning effect.
2. Description of Related Art
At present, most drawers and keyboard supporters in desks and other furniture use rails to support the drawers and keyboard supporter and allow them to be slidable with respect to the furniture item. As shown in FIGS. 7 to 10, a conventional drawer rail has an outer rail (70) fixed to the furniture item (not shown), a sliding rail (73) contained in the outer rail (70), a ball rail (80) contained in the sliding rail (73), and an inner rail (95) fixed to the drawer or the keyboard supporter (not shown). The outer rail (70) has a bottom that is fixed to the furniture item, and a pair of side plates extend upward from the bottom. A plurality of seats (71) are formed on each side plate and each contains a steel outer ball (72). The sliding rail (73) also has a bottom and a pair of side plates extend upward from the bottom. As especially shown in FIG. 9, in the cross sectional view of the sliding rail (73), the bottom has a convex portion (74) and each side plate is substantially S-shaped having an inner groove (75) and an outer groove. The outer balls (72) are rotatably contained in the outer groove to allow the slide rail (73) to be slidable with respect to the outer rail (70). The ball rail (80) also has a bottom and a pair of side plates (81). The bottom has a convex portion (83) corresponding to the convex portion (74) formed in the sliding rail (73). A plurality of steel inner balls (82) are rotatably contained in a plurality of corresponding openings defined in the pair of side plates (81) of the ball rail (80). The inner balls (82) are rotatably contained in the inner groove (75) in the sliding rail (73) to allow the ball rail (80) to be slidable with respect to the sliding rail (73). When the inner balls (82) roll along the inner groove (75), a lower surface of the convex portion (83) is at a certain distance apart from an upper surface of the convex portion (74) of the sliding rail (73). The inner rail (95) has a bottom that is fixed to a drawer and a pair of side plates extend downward from the bottom. The side plates are arcuate to define a groove in which the inner balls (82) can be rotatably contained. The sliding rail (73) has an opening defined therein at an outermost end thereof A positioning device in a form of a rubber pad (90) is inserted in the opening and securely fixed there. The rubber pad (90) has an upper slope (91). When a user pulls the drawer outwardly, the inner rail (95) moves outwardly accordingly. Then the inner balls (82) roll and go outwardly along the inner groove (75) of the sliding rail (73) by frictional contact with the inner rail (95). The inner balls (82) push the ball rail (80) outwardly until a front end (A) of the ball rail (80) meets the slope (91) of the rubber pad (90) and is stopped by a certain friction between the slope (91) and the front end (A). With this friction, the inner rail (95), and thus the drawer or the keyboard supporter, can be positioned with a certain degree of stability. When a user pushes the drawer inwardly, the inner rail (95) moves inwardly. The friction between the inner rail (95) and the inner balls (82) will roll the inner balls (82) to go inwardly along the inner groove (75) of the sliding rail (73). The inner balls (82) push the ball rail (80) inwardly to leave the rubber pad (90).
However, the positioning device of the conventional drawer rail has its drawbacks. When the front end (A) of the ball rail (80) goes outward along the slope (91), it will go upward simultaneously. That means a close requirement in the tolerance must be met between the inner balls (82) and the inner groove (75) of the sliding rail (73) because if the inner balls are over large or the inner groove (75) is over small, the front end (A) of the ball rail (80) can not move upward and downward in a great range which will cause the front end (A) to not be able to go along the slope (19) a distance necessary to provide a sufficient friction. On the other hand, if the inner balls are too small or the inner groove is too large, the front end (A) will be able to move upward and downward in a great range, which will cause the front end (A) to not be able to contact the slope (91) intimately.
The main object of the invention is to provide a positioning device for drawer rail that does not require a close tolerance between the inner balls and the inner groove but is still able to provide a secure positioning effect for the rail.
Other objects, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.